The present invention relates to solar collectors and methods of producing the same.
A typical solar collector absorbs radiant energy by way of an absorber plate to which tubes are mechanically attached or adhesively bonded. A working fluid in the tube transfers useful heat energy from the absorber plate. To attain high efficiency, one strives to achieve good thermal contact between the absorber plate and the tubes. As known in the art, the manner of connecting the tubes to the absorber plate affects heat collecting and transfer efficiency of the solar collector. U.S. patents to Boyd (U.S. Pat. No. 4,074,406), Andrassy (U.S. Pat. No. 4,089,326) Heinman (U.S. Pat. No. 4,245,620), Beckman (U.S. Pat. No. 4,369,836) and Grahman (U.S. Pat. No. 4,517,721) show typical absorber plates with tubes mechanically fastened or cemented into place. Use of dissimilar metals, such as copper tubes and aluminum plates, limits joining and connecting techniques and thereby presents some difficulties in the collector fabrication process.
The present invention improves heat collecting and transfer efficiency regardless of tube configuration, and enables formation of an absorber plate and tube connection with greater thermal contact despite use of dissimilar metals or materials. The invention also obviates the need to use manifolds to connect respective tubes, unlike the welding and mechanical compression techniques used in prior art systems. In addition, an absorber plate having varying thicknesses throughout its surface may conveniently be fabricated.
Solar collectors traditionally include a selective surface to increase absorption efficiency. A common high efficiency selective surface employs electro-plated black nickel or chrome. The process of forming a selective surface involves intricate surface preparation including cleaning, chemical treatment, etching, and electroplating. The present invention, if desired, enables application of a selective surface by conventional techniques, or alternatively, by using metallic foils having a surface which is pre-treated as a selective surface.